This invention relates to a vascular filter system, in particular a vascular filter system having a guide wire, a filter membrane and an umbrella structure, the filter membrane having an inner area provided in the area of the proximal end of the guide wire and a free outer area, and the umbrella structure being made of a flexible material and permitting opening and closing of the umbrella formed by the umbrella structure and filter membrane.
A great number of, for example angioplastic, surgical and non-surgical methods have been developed for removing deposits in blood vessels. These methods, along with the implantation of bypasses at sites affected by stenoses, involve the danger of parts of the plaque or thrombi coming loose and ending in an embolism. In order to prevent such a danger, vascular filters have been developed which are intended to block micro- and macroparticles.
Such a vascular filter is described for example in WO 98/33443. This conventional vascular filter is formed by an opening mechanism. In its open position the filter is substantially perpendicular to the axis of the guide wire via which it can be introduced into the blood vessel. For removal from the blood vessel, conventional vascular filters provide recuperating threads. These can be fastened to the outer circumference of the filter and are operated via a wire which can be guided in the guide wire for example. Recuperation of the filter, e.g. at the end of surgery, requires the application of a sufficient force via the wire connected with the recuperating threads. Since in most methods the site where the filter is introduced into the vessel is far away from the site where the filter is used, the length of the guide wire and recuperating wire is considerable. In surgery on the carotid for example one usually introduces the filter via the artery in the groin. The guide wire and thus also the recuperating wire can thereby have lengths of more than one meter. In order to permit application of the forces necessary for recuperating the filter at a distance of this size, the forces exerted on the recuperating wire must be great.
Due to these great forces and considerable length, as well as the fact that the guide wire must follow the course of the blood vessel and can therefore not be guided through the body straight, the guide wire as well as the recuperating wire and recuperating threads can get caught in conventional vascular filter systems. This can considerably impede and prolong the process of recuperating or folding up and removing the filter. This lengthens the time of the total surgery, which can be serious for the patient, in particular due to the required narcotics. In addition, jammed wires can cause injuries to the blood vessel.
The invention is therefore based on the problem of providing a vascular filter system that does not have the disadvantages of the prior art, is in particular easy and reliable to handle, and reduces the danger of injury to the patient and the strain of longer operating times.
The invention is based on the finding that this problem can be solved by a vascular filter system requiring either no, or a very low, expenditure of force for closing the filter over the length between the site of entry into the body and the site of the filter.
The problem is solved according to the invention by a vascular filter system having contactless means for closing the umbrella.
The inventive vascular filter system is preferably used for non-permanent application.
The inventive system has the advantage that the structure of the umbrella can be simple. No mechanical connections are required between the filter membrane or umbrella structure, on the one hand, and an element extending from the position of the filter to the site where the filter system enters the body, on the other hand. Also, this simple structure prevents a mechanical connection from getting caught, jamming or tearing. This further reduces the risk for the patient. Finally, contactless means can be activated from outside without requiring a great expenditure of force over the length between the position of the filter and the site where the filter system enters the body. This can also prevent injuries or the guide wire and recuperating element getting caught.
In the inventive vascular filter system the umbrella structure is made is a flexible material allowing opening and closing of the umbrella structure. Preferably, the umbrella structure therefore involves a spring which in the released state supports the open umbrella. The spring can consist of a flexible, wire-shaped material bent in a zigzag shape for example, a coil spring or also a flexible wire-shaped material coated with a coil spring. Activation of the umbrella structure material causes the structure to contract, thereby compressing the spring. The spring force of the umbrella structure is preferably selected such that, firstly, sufficient pressure is produced against the wall of the blood vessel in the open state and, secondly, the force for folding up or closing the umbrella is so low that it can be provided by contactless means.
According to an embodiment of the invention, the closing means are given by the umbrella structure material. The umbrella structure is provided at least on the outer area of the filter membrane. If the material of said structure is selected so as to contract under certain circumstances, this causes closing of the umbrella. In this embodiment one can for example use materials which contract through chemical or physical activation, thereby causing closing of the umbrella. Since activation takes place in the blood vessel, i.e. in the body, one must select materials whose activation is safe. One can activate by introducing media into the blood in the area of the filter. Further, one can use materials which contract through the action of radiation.
According to a further embodiment, closing means are additionally provided on the guide wire. These means can cooperate with the means given by the umbrella structure material. The activation of the umbrella structure material necessary for contracting the umbrella structure can in this case be produced by the means provided on the guide wire. The means can either be fastened directly to the guide wire or disposed displaceably thereon.
In the former case, the means are preferably disposed in the area of the guide wire against which the umbrella structure lies after folding up. In the latter case, the means can be fastened for example to a catheter pushed over the guide wire, i.e. carried thereby. In this embodiment it is only necessary to bring the means from a position at a certain distance from the umbrella into the position where it can cooperate with the umbrella structure and closing of the umbrella is effected. The path over which the catheter must be pushed is therefore very small and in particular smaller than the path over which a recuperating wire must be pushed according to the embodiments of the prior art. In addition, for pushing the catheter used according to the invention one need only apply the force for moving the catheter as such. This force is much lower than that necessary for mechanically folding up the umbrella via recuperating wire and recuperating threads against the bloodstream.
According to a preferred embodiment, the means provided on the guide wire are a magnetic catheter. In this embodiment, the magnetic catheter can be threaded onto the guide wire. The magnet is provided on the end of the catheter facing the proximal end of the guide wire. It may be a permanent magnet or else a temporarily activable one, e.g. an electromagnet. In this embodiment the magnetic catheter serves as a displacing element for the magnet as such, thus allowing exact positioning of the magnet with respect to the position of the filter.
According to a further preferred embodiment, the umbrella structure material is activable by temperature changes, i.e. contracts upon a temperature change, thereby causing closing of the umbrella. In this embodiment the umbrella structure is preferably formed from a nitinol spring. This material, which is a Tixe2x80x94Ni alloy, has the advantage of firstly contracting when cold and secondly having a shape memory, i.e. showing a so-called memory effect. The shape in which the umbrella optimally covers the cross section of the blood vessel to be treated can therefore be specified for the umbrella structure, and a contraction of the umbrella structure toward this shape memory obtained by briefly introducing a cold medium, for example ice water.
According to a further embodiment, the umbrella structure material is magnetizable. This quality of the umbrella structure material permits activation of the material by magnetism by means provided on the guide wire. Further, it is possible to form the umbrella structure such that bars of magnetizable material extend radially from the inner area of the filter membrane fastened to the guide wire to the outer area of the filter membrane. For opening the umbrella the bars can be homopolar so that they repel each other, and for closing they can be polarized alternately so that they attract each other.
In a preferred embodiment, the filter system has a guide sheath for receiving the guide wire and umbrella. Said guide sheath can serve firstly to permit the umbrella to be introduced into the blood vessel without injuring the blood vessel, and secondly as a holding device for the closed umbrella upon removal of the filter. The umbrella is preferably withdrawn into the sheath via the guide wire after the closing process and cannot expand again, or only slightly, if the guide sheath diameter is suitably selected. This permits the umbrella to be held in the folded up position without requiring further apparatuses after the closing means are deactivated, e.g. the magnet switched off or the addition of ice water stopped.
The guide sheath can serve in addition as a conduit for media to be brought into the area of the umbrella for effecting activation of the umbrella structure material, i.e. its contraction, e.g. as a conduit for ice water.
The invention will be described further in the following with reference to the enclosed drawing showing possible embodiments of the invention but not restricting the scope of protection.